Researches have been conducted to efficiently use limited frequency resources, and attentions have been focused on a cognitive radio (CR) technology.
Generally, a CR technology reuses limited frequency resources to more efficiently use the frequency resources. In a CR technology, a secondary communication apparatus of a secondary system may periodically or a periodically sense radio resources that are not used in a primary system, to recognize an available frequency resource and receive/transmit data using the recognized available frequency resource.
However, a primary system typically has priority with respect to an available frequency resource. Accordingly, where a signal of the secondary system may collide with a signal of the primary system, it may be necessary for a secondary communication apparatus to stop communication operations or change frequency resources that are being used.
Thus, the secondary communication apparatus may be required to appropriately sense whether a signal of a primary system exists. For example, the secondary communication apparatus may periodically stop communication operations in the secondary system and sense whether a signal of a primary system exists. In this case, however, stopping communication operations to sense a signal of a primary system may waste radio resources such as time resources.
Accordingly, there is a need for a technology enabling a secondary communication apparatus to appropriately sense a signal of a primary system without wasting radio resources. Since a number of communication systems use a multiple input multiple output orthogonal frequency division multiplexing (MIMO OFDM), there is also a need for a technology enabling a secondary communication apparatus to more efficiently sense a signal of a primary system in a communication environment using MIMO OFDM.